[0002] The present invention relates to a receiving technique, and more specifically, to
a technique of diversity-receiving a transmission signal of Orthogonal Frequency Division
Multiplexing (OFDM) system, for example.
[0003] The OFDM system is one of multi-carrier transmission systems that divides a transmission
signal into a plurality of carrier waves to transmit the signal, and is used in various
fields such as digital television broadcasting.
[0004] Diversity receiving is performed in mobile terminals or in-vehicle receiving apparatuses
employing the OFDM system in order to improve a reception quality.
[0005] A receiving apparatus that diversity-receives a transmission signal of OFDM system
performs Fourier transform on a reception signal of each branch to obtain 52 sub-carrier
signals corresponding to 52 sub-carriers from "-26" to "+26" having different frequencies,
as shown in Fig. 15, for each branch for one symbol. A sub-carrier signal of each
branch is combined for each sub-carrier by the algorithm called Maximum Ratio Combining
(MRC) to obtain a combined signal. Before Fourier transform, automatic frequency control
(AFC) that corrects a carrier frequency error is also performed on the reception signal.
[0006] Further, Fast Fourier Transform (FFT) is known as an algorithm that performs Fourier
transform in a high speed, and FFT processing is typically performed in the receiving
apparatus as the Fourier transform.
[0007] Techniques from various viewpoints have been proposed for such a receiving apparatus.
[0008] For example, Japanese Unexamined Patent Application Publication No.
2006-101245 discloses a technique that mitigates the effects given by variations of a frequency
error estimation value for each branch on correction of frequencies. According to
this technique, a signal intensity and a frequency error of a signal of each branch
are detected in AFC performed on the reception signal before FFT processing. The frequency
error of the reception signal of each branch is weighted and combined according to
the signal intensity, and a phase of each branch is corrected based on the combined
frequency error.
[0009] Further, Japanese Unexamined Patent Application Publication Nos.
2006-80624,
2006-253915, and
2010-226233 disclose techniques for improving a quality of a combined signal by modifying a combining
method by MRC. Before describing these techniques, the combining method by MRC will
be described first.
[0010] In the combining method by MRC, a transmission path response (also referred to as
a transmission path power or a transfer function) for each sub-carrier of each branch
is estimated, and a weighting coefficient to a sub-carrier of each branch is determined
based on the transmission path responses that are estimated. A sub-carrier signal
of each branch that is weighted is combined for each sub-carrier. When the k-th sub-carrier
signal of the i-th symbol of the m-th branch that is subjected to FFT processing is
denoted by Sm(i,k), for example, a weighting coefficient Wm(i,k) is calculated for
each Sm(i,k), and combining is performed using a result obtained by multiplying each
Sm(i,k) by the weighting coefficient Wm(i,k) corresponding to this Sm (i, k) .
[0011] The weighting coefficient Wm (i, k) is expressed by expression (1). In the expression
(1), Hm(i,k) denotes a transmission path response (transfer function) of the k-th
sub-carrier of the i-th symbol of the m-th branch, and Hm*(i,k) denotes the complex
conjugation thereof. Further, N denotes the total number of branches.

[0012] When a combined signal of the k-th sub-carrier of the i-th symbol is denoted by D(i,k),
the combined signal D(i,k) can be expressed by expression (2).

[0013] As shown in the expression (1), the weighting coefficient Wm (i, k) depends on the
amplitude of the transmission path response (transfer function) H. Specifically, in
the combining method by MRC, a large weighting coefficient is multiplied by a signal
with large amplitude of the transmission path response H, and the signal of the branch
is enhanced. However, even when the amplitude of the transmission path response H
is large, it does not necessarily mean that the signal of the branch is strong or
the C/N ratio of the branch is good.
[0014] For example, while a signal of one branch has a poor C/N ratio and small amplitude,
the amplitude may increase due to an operation of auto gain control (AGC) and the
amplitude of the transmission path response H may increase. When combining is performed
by the combining method by MRC in such a case, the C/N ratio of the combined signal
becomes poorer than the C/N ratio of the signal of the branch with good C/N ratio
due to an influence of a signal of a branch with poor C/N ratio.
[0015] The techniques disclosed in Japanese Unexamined Patent Application Publication Nos.
2006-80624 and
2006-253915 calculate a carrier to noise ratio (C/N ratio) of a symbol signal of each branch
after FFT processing or a weighted value (first weighted value in Japanese Unexamined
Patent Application Publication Nos.
2006-80624 and
2006-253915) based on the relative ratio of these C/N ratios, and multiply the symbol signal
of the branch and a transmission path response H estimated for the branch by the weighted
value, and then perform combining by MRC.
[0016] The technique disclosed in Japanese Unexamined Patent Application Publication No.
2010-226233 determines a level of an interference wave by calculating a modulation error ratio
(MER) after FFT processing, weights the signal of each sub-carrier by a weighted value
according to the determined level, and then performs MRC combining.
[0017] JP2006054675 discloses an OFDM receiver that is provided with a propagation path estimating part
for estimating propagation path characteristics in the frequency region of each antenna
branch on the basis of the FFT output signals of respective antenna branch processing
units, a signal quality estimating part for estimating the signal quality of each
antenna branch on the basis of the output signal of the propagation path estimating
part, a multiplying part for multiplying the propagation path characteristics and
the signal quality by corresponding branches, and a composition part for performing
weighting composition of the FFT output signals on the basis of the multiplication
result.
[0018] US8126074 discloses a method and apparatus for processing a frequency domain digital Orthogonal
Frequency Division Multiplexing (OFDM) symbol. The method includes generating an estimate
of a channel for each sub-carrier of the frequency domain digital OFDM symbol; generating
channel state information corresponding to each sub-carrier of the frequency domain
digital OFDM symbol; and generating a plurality of demodulated symbols based, at least
in part on, the estimate of the channel for each sub-carrier of the frequency domain
digital Orthogonal Frequency Division Multiplexing (OFDM) symbol, in which each demodulated
symbol corresponding to a given sub-carrier of the frequency domain digital OFDM symbol.
The method further includes performing a soft-decision decoding on each demodulated
symbol to generate a corresponding soft-decision decoded symbol. The soft-decision
decoding of each demodulated symbol is based, at least in part, on the channel state
information corresponding to the given sub-carrier associated with the demodulated
symbol.
[0019] EP1445907 discloses channel estimation method for an OFDM transceiver. The OFDM transceiver
is configured to derive channel state information (CSI) for a communication channel
by processing the preamble of a received OFDM packet. The received packet could be,
for example, an unsolicited data packet or a solicited service packet such as an acknowledgement
packet. The derived CSI information can then applied to the generation of weighted
OFDM packets for transmission over the communication channel. As a result, an improved
effective communication channel may be established between this OFDM transceiver and
another OFDM transceiver. A channel estimation method of the present invention may
be implemented in an access point (AP) or a client terminal (CLT) of a WLAN system.
In either case, the improved communication channel can be used, for example, to extend
the range corresponding to a selected transmission bit rate and/or to increase the
transmission bit rate between the AP and a CLT. In addition or alternatively, the
improved communication channel can be used to reduce emitted RF power and, therefore,
to reduce electrical power consumption.
[0020] The techniques disclosed in Japanese Unexamined Patent Application Publication Nos.
2006-80624 and
2006-253915 obtain the C/N ratio for each symbol after FFT processing, which causes a problem
that a computation amount increases and the size of the receiving apparatus increases.
[0021] The technique disclosed in Japanese Unexamined Patent Application Publication No.
2010-226233 obtains MER for each sub-carrier after FFT processing, which causes a problem that
a computation amount increases and the size of the receiving apparatus increases,
as is similar to the techniques disclosed in Japanese Unexamined Patent Application
Publication Nos.
2006-80624 and
2006-253915.
[0022] Other problems and novel features will be made apparent from description of this
specification and the accompanying drawings.
[0023] According to a first aspect of the present invention, there is provided a receiving
apparatus according to claim 1.
[0024] According to a second aspect of the present invention, there is provided a communication
apparatus according to claim 4.
[0025] According to a third aspect of the present invention, there is provided a communication
system according to claim 5.
[0026] According to a fourth aspect of the present invention, there is provided a receiving
apparatus according to claim 6.
[0027] According to the receiving apparatus in the first or fourth aspect above, it is possible
to improve a quality of a combined signal obtained by maximum ratio combining performed
when a transmission signal of OFDM system is diversity-received with small computation
amount or small circuit size.
[0028] The above and other aspects, advantages and features will be more apparent from the
following description of certain embodiments taken in conjunction with the accompanying
drawings, in which:
Fig. 1 is a diagram showing a receiving apparatus according to a first embodiment;
Fig. 2 is a diagram showing a configuration example of a combining unit in the receiving
apparatus shown in Fig. 1;
Fig. 3 is a diagram showing a frame format of a transmission signal of OFDM system;
Fig. 4 is a diagram showing a receiving apparatus according to a second embodiment;
Fig. 5 is a diagram showing a front end unit in the receiving apparatus shown in Fig.
4;
Fig. 6 is a diagram showing a receiving apparatus according to a third embodiment;
Fig. 7 is a diagram showing an example of LUTs used by a correction coefficient calculation
unit of the receiving apparatus shown in Fig. 6;
Fig. 8 is a flowchart showing calculation processing of correction coefficients by
the correction coefficient calculation unit of the receiving apparatus shown in Fig.
6;
Fig. 9 is a diagram showing a receiving apparatus according to a fourth embodiment;
Fig. 10 is a diagram showing a correction coefficient calculation unit in the receiving
apparatus shown in Fig. 9;
Fig. 11 is a diagram for describing a determination method of thresholds used by the
correction coefficient calculation unit shown in Fig. 10 when selecting a LUT;
Fig. 12 is a flowchart showing processing for determining the thresholds by the correction
coefficient calculation unit shown in Fig. 10;
Fig. 13 is a diagram showing a communication system according to a fifth embodiment;
Fig. 14 is a diagram showing a communication apparatus in the communication system
shown in Fig. 13; and
Fig. 15 is a diagram showing each sub-carrier signal obtained by FFT conversion.
[0029] For the sake of clarity of description, the following description and the drawings
are omitted and simplified as appropriate. Further, each element shown in the drawings
as a functional block that performs various processing can be configured by a CPU,
a memory, or another circuit in hardware, and is achieved by a program loaded to the
memory in software. Accordingly, a person skilled in the art would understand that
these functional blocks may be achieved in various ways (e.g., only by hardware, only
by software, or the combination thereof) without any limitation. Throughout the drawings,
the same elements are denoted by the same reference symbols, and overlapping description
is omitted as appropriate.
[0030] The program can be stored and provided to a computer using any type of non-transitory
computer readable media. Non-transitory computer readable media include any type of
tangible storage media. Examples of non-transitory computer readable media include
magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.),
optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (compact disc
read only memory), CD-R (compact disc recordable), CD-R/W (compact disc rewritable),
and semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable
PROM), flash ROM, RAM (random access memory), etc.). The program may be provided to
a computer using any type of transitory computer readable media. Examples of transitory
computer readable media include electric signals, optical signals, and electromagnetic
waves. Transitory computer readable media can provide the program to a computer via
a wired communication line (e.g. electric wires, and optical fibers) or a wireless
communication line.
[0031] Any one of the following embodiments relates to a technique of diversity-receiving
a transmission signal of OFDM system, and the total number of branches is two, for
example. As a matter of course, the technique according to these embodiments may be
applied to a case in which the total number of branches is any number equal to or
larger than two.
<First embodiment>
[0032] Fig. 1 shows a receiving apparatus 100 according to a first embodiment. The receiving
apparatus 100 diversity-receives a transmission signal of OFDM system. The receiving
apparatus 100 includes, for a first branch, an antenna 110, a front end unit 112,
an FFT processing unit 114, and a transmission path response estimation unit 116,
and for a second branch, an antenna 120, a front end unit 122, an FFT processing unit
124, and a transmission path response estimation unit 126. The receiving apparatus
100 further includes a correction coefficient calculation unit 130 and a combining
unit 140. Other functional blocks typically included in this type of receiving apparatus,
e.g. , a decoder that performs Viterbi decoding on a combined signal D output from
the combining unit 140, are omitted in Fig. 1.
[0033] First, the first branch of the receiving apparatus 100 will be described.
[0034] A signal received by the antenna 110 (reception signal R1 of the first branch) is
input to the front end unit 112. The front end unit 112 performs A/D conversion, AGC
processing, filter processing, CFO estimation (CFO: CARRIER FREQUENCY OFFSET), synchronization
processing or the like on the reception signal R1. A digital signal obtained by the
front end unit 112 is input to the FFT processing unit 114.
[0035] The FFT processing unit 114 as a Fourier transformer performs FFT processing on the
digital signal from the front end unit 112 to convert a time-domain OFDM symbol signal
of the first branch into a frequency-domain OFDM symbol signal. One OFDM symbol signal
obtained by the FFT processing unit 114 includes a plurality of signals (sub-carrier
signals) corresponding to a plurality of (e.g., 52) sub-carriers. Hereinafter, each
sub-carrier signal of the first branch is denoted by "S1".
[0036] Each sub-carrier signal S1 obtained by the FFT processing unit 114 is input to the
combining unit 140, and is also input to the transmission path response estimation
unit 116.
[0037] The transmission path response estimation unit 116 estimates, for each sub-carrier
signal S1, a transmission path response to output the transmission path response to
the combining unit 140. The transmission path response obtained by the transmission
path response estimation unit 116 is denoted by "H1".
[0038] In the similar way for the second branch, a signal received by the antenna 120 (reception
signal R2 of the second branch) is first input to the front end unit 122. The front
end unit 122 performs A/D conversion, AGC processing, filter processing, CFO estimation,
synchronization processing or the like on the reception signal R2, as is similar to
the front end unit 112. A digital signal obtained by the front end unit 122 is input
to the FFT processing unit 124.
[0039] The FFT processing unit 124 as a Fourier transformer performs FFT processing on the
digital signal from the front end unit 122 to convert a time-domain OFDM symbol signal
of the second branch into a frequency-domain OFDM symbol signal. One OFDM symbol signal
obtained by the FFT processing unit 124 also includes a plurality of sub-carrier signals
corresponding to respective sub-carriers. Hereinafter, each sub-carrier signal of
the second branch is denoted by "S2".
[0040] Each sub-carrier signal S2 obtained by the FFT processing unit 124 is input to the
combining unit 140, and is also input to the transmission path response estimation
unit 126.
[0041] The transmission path response estimation unit 126 estimates, for each sub-carrier
signal S2, a transmission path response to output the transmission path response to
the combining unit 140. The transmission path response obtained by the transmission
path response estimation unit 126 is denoted by "H2".
[0042] The combining unit 140 performs combining on the sub-carrier signal S1 output from
the FFT processing unit 114 and the sub-carrier signal S2 output from the FFT processing
unit 124 for each sub-carrier to obtain a combined signal D.
[0043] In this type of conventional receiving apparatus, a functional block corresponding
to the combining unit 140 obtains a weighting coefficient for each branch from the
transmission path response H1 and the transmission path response H2 by maximum ratio
combining (hereinafter referred to as "MRC combining") to perform a weighted addition
on the sub-carrier signal S1 and the sub-carrier signal S2. An operation expression
of the weighted addition by maximum ratio combining will hereinafter be referred to
as a "maximum ratio combining operation expression". This maximum ratio combining
operation expression is expression (3). Note that the expression (3) is the one in
which the aforementioned expression (2) is applied to the case of two branches. The
symbols "i" and "k" in the expression (3) denote the number of symbol and the number
of sub-carrier, respectively, and the symbols "m" and "j" each denote the number of
branch. The same holds true for the following expressions.

[0044] As will be clear from the expression (3), in this type of conventional receiving
apparatus, the weighting coefficient in MRC combining is calculated based on the transmission
path response of each branch.
[0045] Meanwhile, the receiving apparatus 100 according to this embodiment further includes
the correction coefficient calculation unit 130, and the combining unit 140 performs
a weighted addition after correcting the weighted coefficient shown by the expression
(3) with the correction coefficient (α1(i), α2(i)) obtained for each branch by the
correction coefficient calculation unit 130. Before describing a specific operation
by the combining unit 140, the correction coefficient calculation unit 130 will be
described first.
[0046] The correction coefficient calculation unit 130 obtains the correction coefficient
according to the magnitude relation of the intensity of the reception signal of each
branch (reception signal R1, reception signal R2). The correction coefficient is smaller
in branches with smaller reception signal intensities. The correction coefficients
of the first branch and the second branch obtained by the correction coefficient calculation
unit 130 are denoted by a first correction coefficient α1 and a second correction
coefficient α2, respectively.
[0047] When the correction coefficient is calculated, the correction coefficient calculation
unit 130 adds a maximum correction coefficient for the branch which has the largest
reception signal intensity (hereinafter referred to as a "strongest branch"), for
example, and for each of the other branches, obtains a correction coefficient equal
to or smaller than the maximum correction coefficient according to the difference
in the intensity between the branch and the strongest branch. Description will now
be made taking a case in which the maximum correction coefficient is "1" as an example.
[0048] First, a case in which the reception signal intensity is measured from the reception
signal R1 and the reception signal R2 before A/D conversion will be described. In
an analog signal before A/D conversion, it is impossible to know which symbol it corresponds
to. One method in this case is to apply the correction coefficient calculated from
the reception signal intensity that is measured to all the following symbols.
[0049] In this case, the correction coefficient calculation unit 130 calculates the first
correction coefficient α1 and the second correction coefficient α2 according to the
following expression (4A).

[0050] In expression (4A), "Q1" and "Q2" denote the reception signal intensities of the
reception signal R1 and the reception signal R2, respectively, and "diffA" denotes
an absolute value of the difference between the reception signal intensity Q1 and
the reception signal intensity Q2.
[0051] As will be clear from the expression (4A), when the branch which has a large reception
signal intensity (strongest branch) is the first branch (Q1>=Q2), the correction coefficient
calculation unit 130 adds the maximum correction coefficient "1" to the first branch.
Thus, the first correction coefficient α1 becomes "1". Further, the correction coefficient
calculation unit 130 calculates, for the second branch, the second correction coefficient
α2 from "diffA".
[0052] On the other hand, when the strongest branch is the second branch ("else" or "Q1<Q2"),
the correction coefficient calculation unit 130 adds the maximum correction coefficient
"1" to the second branch. Thus, the second correction coefficient α2 (i) becomes "1".
Further, the correction coefficient calculation unit 130 calculates, for the first
branch, the first correction coefficient α1 from "diffA".
[0053] For example, the reception signal intensities of the reception signal R1 and the
reception signal R2 before A/D conversion are continuously measured, and when there
is no change in the intensities, the correction coefficients obtained from the reception
signal intensities that are measured are applied to all the symbols. Meanwhile, when
there is a change in the reception signal intensities, the correction coefficients
obtained from the reception signal intensities after the change may be applied to
the following symbols.
[0054] Alternatively, the reception signal intensities of the reception signal R1 and the
reception signal R2 before A/D conversion are periodically measured at some predetermined
interval, and the correction coefficients may be updated every time the measurement
is made.
[0055] In order to obtain a better correction effect, it is preferable to measure the reception
signal intensity of the reception signal of each branch for each symbol to obtain
the correction coefficient for each symbol. In this case, the measurement of the intensities
of the reception signals is performed after A/D conversion and synchronization processing.
[0056] Specifically, for example, it is possible to obtain the reception signal intensity
of each symbol of each branch based on the reception signal intensities obtained when
the front end unit 112 and the front end unit 122 perform AGC processing. The reception
signal intensity obtained when the AGC processing is performed corresponds to the
reception signal intensity of the short preamble included in the synchronization signal
of the top of each frame. Accordingly, by measuring a variation amount of the received
power with elapse of time from the short preamble for each frame and adding the resulting
variation amount to the reception signal intensity of the frame, it is possible to
obtain the reception signal intensity of each symbol of the frame. The reception signal
intensities obtained in the AGC processing will be described later in detail in the
second embodiment.
[0057] In this case, the correction coefficient calculation unit 130 calculates the first
correction coefficient α1 and the second correction coefficient α2 according to the
following expression (4B), for example.

[0058] In the expression (4B), "Q1(i)" and "Q2(i)" denote the intensity of the i-th symbol
in the reception signal R1 and the intensity of the i-th symbol in the reception signal
R2 after A/D conversion, respectively, and "diffA(i)" denotes an absolute value of
the difference between the intensity Q1(i) and the intensity Q2(i).
[0059] As will be clear from the expression (4B), when the strongest branch is the first
branch (Q1(i)>=Q2(i)), the correction coefficient calculation unit 130 adds the maximum
correction coefficient "1" to the first branch. Thus, the first correction coefficient
α1(i) becomes "1". Further, the correction coefficient calculation unit 130 calculates,
for the second branch, the second correction coefficient α2(i) from "diffA(i)".
[0060] Meanwhile, when the strongest branch is the second branch ("else" or "Q1(i)<Q2(i)",
the correction coefficient calculation unit 130 adds the maximum correction coefficient
"1" to the second branch. Thus, the second correction coefficient α2(i) becomes "1".
Further, the correction coefficient calculation unit 130 calculates, for the first
branch, the first correction coefficient α1(i) from "diffA(i)".
[0061] Each of the symbols Q1(i) and Q2 (i) that are the intensities of the i-th symbols
in the reception signal R1 and the reception signal R2 may be, for example, the average
intensity in the time axis of the symbol, the intensity at any position of the symbol
(e.g., top or middle point).
[0062] When combining the sub-carrier signals S1 and S2 by a weighted addition, the combining
unit 140 obtains a weighting coefficient so as to weaken an influence of the transmission
path response of the sub-carrier signal of the branch in branches with smaller correction
coefficients obtained by the correction coefficient calculation unit 130 to perform
combining. Some specific examples of the combining method by the combining unit 140
will now be described. An expression indicating the operation by the combining unit
140 will hereinafter be referred to as a "combining operation expression".
[0063] For example, the combining unit 140 corrects each term of the numerator and the denominator
of the maximum ratio combining operation expression (expression (3)) with a correction
coefficient calculated for the branch corresponding to the term by the correction
coefficient calculation unit 130.
[0064] Specifically, for example, as shown in expression (5) which is a combining operation
expression, the combining unit 140 multiplies each term of the numerator and the denominator
of the maximum ratio combining operation expression by the correction coefficient
of the branch corresponding to the term.

[0065] Alternatively, the combining unit 140 may correct, as shown in a combining operation
expression shown in expression (6), the transmission path response of each branch
by multiplying it by the correction coefficient of the branch, to combine the sub-carrier
signal of each branch at a maximum ratio using the transmission path response of each
branch after the correction.

[0066] Fig. 2 shows a configuration example of the combining unit 140. The combining unit
140 shown in Fig. 2 performs a weighted addition on the sub-carrier signal S1 and
the sub-carrier signal S2 by the operation shown in the expression (5), and includes
a multiplication unit 151, a power calculation unit 152, a multiplier 153, a multiplier
154, a multiplier 161, a power calculation unit 162, a multiplier 163, a multiplier
164, an adder 171, an adder 172, and a divider 173.
[0067] The multiplication unit 151 multiplies the sub-carrier signal S1 by a complex conjugation
of the transmission path response H1 to output the obtained value to the multiplier
153. The power calculation unit 152 calculates the square of the amplitude of the
transmission path response H1 (|H1|
2) to output the obtained value to the multiplier 154. The multiplier 153 multiplies
the first correction coefficient α1 from the correction coefficient calculation unit
130 by the output from the multiplication unit 151 to output the obtained value to
the adder 171. The output from the multiplier 153 is one term of the two terms of
the numerator part in expression (5). Further, the multiplier 154 multiplies the first
correction coefficient α1 by the output from the power calculation unit 152 to output
the obtained value to the adder 172. The output from the multiplier 154 is one term
of the two terms of the denominator part in expression (5).
[0068] The multiplier 161 multiplies the sub-carrier signal S2 by a complex conjugation
of the transmission path response H2 to output the obtained value to the multiplier
163. The power calculation unit 162 calculates the square of the amplitude of the
transmission path response H2 (|H2|
2) to output the obtained value to the multiplier 164. The multiplier 163 multiplies
the second correction coefficient α2 from the correction coefficient calculation unit
130 by the output from the multiplication unit 161 to output the obtained value to
the adder 171. The output from the multiplier 163 is the other term of the two terms
of the numerator part in expression (5). The multiplier 164 multiplies the second
correction coefficient α2 by the output from the power calculation unit 162 to output
the obtained value to the adder 172. The output from the multiplier 164 is the other
term of the two terms of the denominator part in expression (5).
[0069] The adder 171 adds outputs of the multiplier 153 and the multiplier 163 to obtain
the numerator part in expression (5), and the adder 172 adds outputs of the multiplier
154 and the multiplier 164 to obtain the denominator part in expression (5). The divider
173 then divides the output from the adder 171 by the output from the adder 172 to
obtain the combined signal D.
[0070] As will be clear from the description above, the combining unit 140 corrects the
weighting coefficient of the maximum ratio combining so as to weaken the influence
of the transmission path response estimated for the sub-carrier signal of the branch
in branches with smaller reception signal intensities according to the magnitude relation
of the intensity of the reception signal of each branch before FFT processing.
[0071] It is generally considered that, the lower the intensity of the reception signal
is, the smaller a signal to noise ratio (SNR) is. When combining the sub-carrier signal
of each branch for each sub-carrier at a maximum ratio, the receiving apparatus 100
according to this embodiment weakens the influence given by the transmission path
response estimated for the branch on the weighting coefficient in branches with smaller
reception signal intensities or smaller SNR according to the magnitude relation of
the intensities of the reception signals between branches, thereby being able to improve
the quality of the combined signal D.
[0072] Further, the receiving apparatus 100 acquires correction coefficients according to
the intensities of the reception signals before Fourier operation, and applies the
same correction coefficients to all the sub-carrier signals included in the same symbol.
It is therefore not required to obtain the C/N ratio for each symbol unlike the techniques
disclosed in Japanese Unexamined Patent Application Publication Nos.
2006-80624 and
2006-253915, and to obtain MER for each sub-carrier as disclosed in Japanese Unexamined Patent
Application Publication No.
2010-226233. It is therefore possible to suppress increases in the computation amount and the
circuit size.
[0073] Furthermore, the technique disclosed in Japanese Unexamined Patent Application Publication
No.
2010-226233 requires calculation of MER for each sub-carrier. In order to obtain MER, it is required
to compare an ideal constellation position with IQ positions (positions in an IQ coordinate
system) for each sub-carrier to obtain the difference. It is possible to determine
MER with some extent of accuracy even with low SNR when the modulation system of Binary
Phase Shift Keying (BPSK) / Quaternary Phase Shift Keying (QPSK) is used. When the
modulation system of Quadrature Amplitude Modulation (QAM) is used, however, intervals
between constellation points are narrow. When the SNR is low, there is a high possibility
that comparison is made with a non-ideal constellation position, which degrades the
calculation accuracy of MER. The effect of this technique thus depends on the modulation
system, and some modulation systems may reduce a quality of a combined signal.
[0074] Meanwhile, the receiving apparatus 100 according to this embodiment obtains the correction
coefficient of each branch according to the intensities of the reception signals before
Fourier transform, thereby being able to improve the quality of the combined signal
without depending on the modulation system.
<Second embodiment>
[0075] Before describing a second embodiment, a frame format of a transmission signal of
OFDM system will be described first.
[0076] Fig. 3 shows a frame format of a transmission signal of OFDM system. For the sake
of clarity, in Fig. 3, GUARD INTERVAL (GI) provided between regions is omitted.
[0077] As shown in Fig. 3, one frame of the transmission signal of OFDM system includes
a synchronization signal part, a header, and a service data part arranged in time
series. The synchronization signal part includes a short preamble and a long preamble.
The header includes information including a data rate and a data length. The service
data part includes a plurality of pieces of data (divided data) from the top DATA1
to the last DATA LAST. The header corresponds to one symbol, and one piece of divided
data also corresponds to one symbol.
[0078] The receiving apparatus 100 according to the first embodiment described above obtains
a correction coefficient of each branch according to the magnitude relation of the
intensity of the reception signal of each branch before Fourier transform to use the
correction coefficients when obtaining a combined signal after Fourier transform.
[0079] When measuring the reception intensities from the reception signals before A/D conversion,
for example, the receiving apparatus 100 measures the intensity of the reception signal
of each branch, and uses the correction coefficient obtained according to the measured
intensity for combination of each of the following symbols.
[0080] Alternatively, when obtaining the correction coefficient for each symbol of each
branch, for example, the receiving apparatus 100 obtains, for one symbol ("DATA1"),
the correction coefficient for each branch according to the magnitude relation of
the intensity of the symbol "DATA1" of each branch. The receiving apparatus 100 then
corrects, when performing a weighted addition on the sub-carrier signal of each branch
for each sub-carrier for the symbol "DATA1" after Fourier operation, the weighting
coefficient of each branch with the correction coefficient obtained for each branch.
[0081] Further, for another symbol ("DATA2"), the correction coefficient is obtained for
each branch according to the magnitude relation of the intensity of the symbol in
the reception signal of each branch. The receiving apparatus 100 then corrects, when
performing a weighted addition on the sub-carrier signal of each branch for each sub-carrier
for the symbol "DATA2" after Fourier operation, the weighting coefficient of each
branch with the correction coefficient obtained for each branch.
[0082] In summary, in this case, the receiving apparatus 100 obtains the correction coefficient
of each branch for each symbol, and uses each correction coefficient that is obtained
to combine the sub-carrier signal corresponding to the symbol.
[0083] The aforementioned correction coefficient may be obtained for each frame, not for
each symbol. For example, according to the magnitude relation of the intensity of
each frame corresponding to each branch before Fourier transform and after synchronization
processing, smaller correction coefficients are obtained in branches with smaller
frame intensities. When the sub-carrier signals are combined, each correction coefficient
thus obtained is applied to all the symbols of the frame.
[0084] The "intensity of the frame" may be, for example, the intensity of a predetermined
part of the frame (e.g., synchronization signal part).
[0085] According to this technique, it is sufficient that one correction coefficient is
calculated for one frame, thereby being able to reduce the computation amount compared
to the case in which the correction coefficient is obtained for each symbol.
[0086] More preferably, the intensity of the short preamble is regarded as the intensity
of the frame, the correction coefficient is obtained from the intensity of the short
preamble of each branch, and the correction coefficients are applied to all the symbols
of the frame. In such a case, it is possible to further suppress the circuit size
and the computation amount to obtain the correction coefficients. The reason for this
will now be described.
[0087] In the receiving apparatus that receives a transmission signal of OFDM system, a
reception signal is converted into a digital signal by A/D conversion, and the digital
signal is then subjected to a Fourier transform. In order to obtain a sub-carrier
signal of optimal amplitude that is easily demodulated, in A/D conversion, adjustment
of a gain is typically performed by processing called Auto Gain Control (AGC).
[0088] The aforementioned AGC is performed based on the signal of the short preamble part.
In short, the gain of the frame at the time of the A/D conversion is determined according
to the intensity of the short preamble.
[0089] In summary, the reception signal intensity of the short preamble is obtained in the
AGC. Accordingly, when the correction coefficient is obtained using the reception
signal intensity of the short preamble obtained in the AGC, there is no need to additionally
provide means for obtaining the intensity of the reception signal, thereby being able
to reduce the computation amount and the circuit size.
[0090] Based on the aforementioned description, the second embodiment will be described.
[0091] Fig. 4 shows a receiving apparatus 200 according to the second embodiment. The receiving
apparatus 200 also diversity-receives a transmission signal of OFDM system, and is
similar to the receiving apparatus 100 except that a correction coefficient calculation
unit 230 and a combining unit 240 are provided in place of the correction coefficient
calculation unit 130 and the combining unit 140. Only the points related to the correction
coefficient calculation unit 230 and the combining unit 240 of the receiving apparatus
200 will be described here.
[0092] In the receiving apparatus 200, the correction coefficient calculation unit 230 obtains,
for each frame, the correction coefficient of each branch based on the reception signal
intensities obtained when the front end unit 112 and the front end unit 122 perform
AGC processing to output the correction coefficients to the combining unit 240.
[0093] Hereinafter, the reception signal intensities obtained when the front end unit 112
and the front end unit 122 perform AGC processing are denoted by RSSI1 (n) and RSSI2
(n), respectively, and the correction coefficients calculated for the first branch
and the second branch by the correction coefficient calculation unit 230 are denoted
by α1(n) and α2(n), respectively. The symbol n denotes the number of the frame.
[0094] The front end unit 112 and the front end unit 122 are similar to those typically
included in this type of receiving apparatus. These configurations will be described
taking the front end unit 112 as an example.
[0095] Fig. 5 shows the front end unit 112. The front end unit 112 includes an A/D converter
211, an AGC unit 212, a filter 213, an LP position estimation unit 214, an AFC unit
215, and a phase correction unit 216.
[0096] The A/D converter 211 is shown as ADC in Fig. 5, and converts the reception signal
R1 of the first branch into a digital signal.
[0097] The AGC unit 212 performs AGC based on the amplitude of the short preamble part in
the digital signal output from the A/D converter 211, to adjust the gain of the reception
signal R1 supplied to the A/D converter 211. Further, in AGC, the AGC unit 212 obtains
RSSI1(n). In this exemplary embodiment, this RSSI1(n) is output to the correction
coefficient calculation unit 230.
[0098] The filter 213 is a low-pass filter, filters the digital signal from the A/D converter
211, and outputs the filtered signal to the LP position estimation unit 214 (LP: Long
Preamble) and the AFC unit 215.
[0099] The LP position estimation unit (in Fig. 5, TD: TIMING DETECTION) 214 detects the
last position of the short preamble from the signal output from the filter 213, estimates
the start position of the long preamble, and notifies the FFT processing unit 114
of the start position.
[0100] The AFC unit (in Fig. 5, AFC: Automatic Frequency Control) 215 estimates a CFO using
the short preamble and the long preamble in the signal output from the filter 213.
[0101] The phase correction unit (in Fig. 5, PS: PHASE SHIFT) 216 performs phase correction
on the signal output from the filter 213 based on the CFO estimated by the AFC unit
215.
[0102] The information indicating the start position of the long preamble estimated by the
LP position estimation unit 214 and the signal obtained by correcting the phase by
the phase correction unit 216 are input to the FFT processing unit 114. The FFT processing
unit 114 performs FFT processing on the signal output from the filter 213 based on
the start position of the long preamble estimated by the LP position estimation unit
214, to obtain the sub-carrier signal S1 of each symbol of the frame.
[0103] The front end unit 122 performs the similar processing as the front end unit 112
on the reception signal R2 of the second branch. As a result, RSSI2 (n) is obtained
from the front end unit 122. This RSSI2(n) is also output to the correction coefficient
calculation unit 230.
[0104] Referring back to Fig. 4, description will be made.
[0105] The correction coefficient calculation unit 230 calculates, for each frame, the correction
coefficient which becomes smaller in branches with smaller reception signal intensities
according to the magnitude relation between RSSI1(n) and RSSI2(n).
[0106] For example, the correction coefficient calculation unit 230 adds, for the branch
which has the largest reception signal intensity (strongest branch), the maximum correction
coefficient, and obtains, for each of the other branches, the correction coefficient
which is equal to or smaller than the maximum correction coefficient according to
the difference in the intensity between the branch and the strongest branch. Now,
description will be made taking a case in which the maximum correction coefficient
is "1" as an example.
[0107] In this case, the correction coefficient calculation unit 230 calculates the first
correction coefficient α1(n) and the second correction coefficient α2(n) according
to the following expression (7), for example.

[0108] As will be clear from the expression (7), for the n-th frame, when the strongest
branch is the first branch (RSSI1 (n) >=RSSI2(n)), the correction coefficient calculation
unit 230 adds the maximum correction coefficient "1" to the first branch. Thus, the
first correction coefficient α1(n) becomes "1". Further, the correction coefficient
calculation unit 230 calculates, for the second branch, the correction coefficient
(α2(n)) from the absolute value "diffA(n)" of the difference between RSSI1(n) and
RSSI2(n).
[0109] On the other hand, when the strongest branch is the second branch ("else" or "RSSI1
(n) <RSSI2 (n)"), the correction coefficient calculation unit 230 adds the maximum
correction coefficient "1" to the second branch. Thus, the second correction coefficient
α2(n) becomes "1". Further, the correction coefficient calculation unit 230 calculates,
for the first branch, the correction coefficient (α1(n)) from "diffA(n)".
[0110] When combining the sub-carrier signals S1 and S2 by a weighted addition, the combining
unit 240 obtains a weighting coefficient so as to weaken the influence of the transmission
path response of the sub-carrier signal of the branch in branches with smaller correction
coefficients obtained by the correction coefficient calculation unit 230 to perform
combining.
[0111] In the receiving apparatus 100, the combining unit 140 applies the correction coefficient
calculated for each symbol by the correction coefficient calculation unit 130 to each
sub-carrier of the symbol. Meanwhile, the combining unit 240 applies the correction
coefficient calculated for each frame by the correction coefficient calculation unit
230 to each sub-carrier of all the symbols of the frame. Except for this point, the
specific combining method by the combining unit 240 is similar to that in the combining
unit 140.
[0112] Expressions (8) and (9) are examples of combining operation expressions used by the
combining unit 240 when performing combining operations. These expressions (8) and
(9) correspond to the combining operation expressions by the combining unit 140 (expressions
(5) and (6)), respectively.

[0113] As will be clear from the expressions (8) and (9), in the combining unit 240, the
correction coefficients (α1(n) and α2(n)) calculated for each frame by the correction
coefficient calculation unit 230 are applied to all the sub-carriers of all the symbols
of the frame.
[0114] In this way, the receiving apparatus 200 is able to obtain each effect of the receiving
apparatus 100 and to further reduce the computation amount compared to the receiving
apparatus 100.
<Third embodiment>
[0115] In an environment in which received power (intensity of a reception signal) is generally
low, SNR of a reception signal in either branch is relatively low. Thus a quality
of a combined signal obtained by maximum ratio combining is degraded due to an influence
of the branch having lower SNR among these branches. The aforementioned receiving
apparatus 100 and the receiving apparatus 200 solve this problem by correcting each
term of the maximum ratio combining operation expression with the correction coefficient
according to the magnitude relation of the intensity of the reception signal of each
branch.
[0116] On the other hand, in an environment in which received power is generally high, SNR
of a reception signal in either branch is relatively high. When the environment with
high received power is compared with the environment with low received power for one
branch, a degree that the branch degrades the combined signal is lower in the environment
with high received power even when the difference between the received power of the
branch and the received power of the strongest branch is the same.
[0117] Further, in fading environments such as in mobile terminals or in-vehicle receiving
apparatuses, the magnitude relation of the intensity of the synchronization signal
part of the reception signal does not necessarily match the magnitude relation of
the intensity of the reception signal of the service data part between branches. Due
to this reason, when the correction coefficients obtained according to the magnitude
relation of the intensity of the synchronization signal part of the reception signal
of the frame corresponding to each branch are applied to all the symbols of the frame,
this may cause degradation in the quality of the combined signal. This problem is
more significant in environments with high received power.
[0118] In order to solve this problem, the receiving apparatus 300 according to the third
embodiment is obtained by improving the performance of the receiving apparatus 200.
As shown in Fig. 6, the receiving apparatus 300 is similar to the receiving apparatus
200 except that the correction coefficient calculation unit 330 is provided in place
of the correction coefficient calculation unit 230. Accordingly, only the correction
coefficient calculation unit 330 of the receiving apparatus 300 will be described.
[0119] Before describing a specific configuration of the correction coefficient calculation
unit 330, a method of calculating correction coefficients by the correction coefficient
calculation unit 330 will be described first.
[0120] The correction coefficient calculation unit 330 calculates, as is similar to the
correction coefficient calculation unit 230 in the receiving apparatus 200, for each
branch, a correction coefficient of each branch based on the reception signal intensity
of each branch. Further, the correction coefficient calculation unit 330 adds the
maximum correction coefficient "1" for the branch which has the largest reception
signal intensity (strongest branch), and for each of the other branches, obtains the
correction coefficient which is equal to or smaller than 1 according to the difference
in the intensities of the reception signals of the branch and the strongest branch.
This point is also similar to the correction coefficient calculation unit 230.
[0121] When the correction coefficient calculation unit 230 is used, the same correction
coefficients are obtained if the difference in the intensities of the reception signals
between each of the branches and the strongest branch is the same. On the other hand,
when the correction coefficient calculation unit 330 is used, different correction
coefficients are obtained when the intensity of the reception signal of the strongest
branch itself is different even when the difference in the intensities of the reception
signals between each of the branches and the strongest branch is the same.
[0122] More specifically, the correction coefficient calculation unit 330 obtains correction
coefficients so that the correction coefficients are larger as the intensity of the
reception signal of the strongest branch is larger under a condition that the correction
coefficient becomes smaller as the difference in the intensities of the reception
signals between each of the branches other than the strongest branch and the strongest
branch is larger. Expression (10) shows one example of calculation methods by the
correction coefficient calculation unit 330.

[0123] As will be clear from the expression (10), when the strongest branch is the first
branch for the n-th frame (RSSI1 (n) >=RSSI2(n)), the correction coefficient calculation
unit 330 adds the maximum correction coefficient "1" to the first branch. Thus, the
first correction coefficient α1(n) becomes "1". Further, the correction coefficient
calculation unit 330 calculates, for the second branch, the correction coefficient
(α2(n)) from diffB(n) (hereinafter referred to as a "difference B") obtained by subtracting
the offset value (offset in the expression) from the absolute value "diffA(n)" of
RSSI1(n) and RSSI2(n). When the correction coefficient α2(n) that is calculated is
larger than 1, the correction coefficient calculation unit 330 sets the correction
coefficient α2(n) to "1".
[0124] Meanwhile, when the strongest branch is the second branch ("else" or "RSSI1(n)<RSSI2(n)"),
the correction coefficient calculation unit 330 adds the maximum correction coefficient
"1" to the second branch. Thus, the second correction coefficient α2(n) becomes "1".
Further, the correction coefficient calculation unit 330 calculates, for the first
branch, the correction coefficient (α1(n)) from the difference B(diffB(n)) obtained
by subtracting the offset value from "diffA(n) ". When the correction coefficient
α1(n) that is calculated is larger than 1, the correction coefficient calculation
unit 330 sets the correction coefficient α1(n) to "1".
[0125] The offset value in the expression (10) is a value equal to or larger than 0 set
according to the intensity of the reception signal of the strongest branch. Specifically,
a larger offset value is set as the intensity of the reception signal of the strongest
branch is larger.
[0126] Accordingly, the difference B used to obtain the correction coefficient becomes smaller
than the original difference diffA(n) as the intensity of the reception signal of
the strongest branch becomes larger. Thus, the correction coefficient becomes larger
than the correction coefficient calculated by diffA(n).
[0127] Specifically, the correction coefficient calculation unit 330 uses the intensity
of the reception signal of the strongest branch as an index value indicating the intensity
of the received power of the whole reception environment, and as the intensity of
the reception signal of the strongest branch becomes larger, the correction intensity
by the correction coefficient obtained from the intensity of the reception signal
of each of the other branches is weakened.
[0128] According to this operation, it is possible to correct the weighting coefficient
according to the strength of the received power of the whole reception environment
when the combined signal is obtained, thereby being able to further increase the quality
of the combined signal and to suppress degradation of the quality of the combined
signal also in a fading environment.
[0129] Based on the aforementioned description, a specific configuration of the correction
coefficient calculation unit 330 will be described.
[0130] As shown in Fig. 6, the correction coefficient calculation unit 330 includes a LUT
storage unit 340 and a LUT selection unit 350.
[0131] The LUT storage unit 340 stores a plurality of look up tables (LUTs). Each of the
LUTs associates the correction coefficient and diffA to calculate the correction coefficient
of each of the branches other than the strongest branch.
[0132] Fig. 7 shows an example of four LUTs (LUT1 to LUT4) stored in the LUT storage unit
340. LUT1 is a correction coefficient calculated for each diffA (the absolute value
of the difference in the intensities of the reception signals between each of the
branches and the strongest branch) according to the expression (10) when the offset
is set to 0 dB. LUT2 is a correction coefficient calculated for each diffA according
to the expression (10) when the offset is set to 5 dB. LUT3 is a correction coefficient
calculated for each diffA according to the expression (10) when the offset is set
to 10 dB. LUT4 is a correction coefficient calculated for each diffA according to
the expression (10) when the offset is set to 15 dB. While the number of LUTs is not
limited to four, about four LUTs are appropriately provided since further increase
in the number of LUTs approaches properties of single reception too much.
[0133] The LUT selection unit 350 in the CORRECTION COEFFICIENT CALCULATION UNIT 330 selects
one of LUT1 to LUT4 according to the intensity of the reception signal of the strongest
branch (RSSI(max)). For example, when RSSI (max) is equal to or smaller than the threshold
T1, the LUT selection unit 350 selects LUT (LUT1) corresponding to the minimum offset
(0 dB).
[0134] Further, when RSSI (max) is larger than the threshold T1 and is equal to or smaller
than the threshold T2, the LUT selection unit 350 selects a LUT (LUT2) corresponding
to the second smallest offset (5 dB). Similarly, when RSSI(max) is larger than the
threshold T2 and is equal to or smaller than the threshold T3, the LUT selection unit
350 selects LUT3, and when RSSI(max) is larger than the threshold T3, the LUT selection
unit 350 selects LUT4 corresponding to the maximum offset (15 dB).
[0135] The correction coefficient calculation unit 330 adds the correction coefficient "1"
for the strongest branch, and for each of the other branches, obtains the correction
coefficient corresponding to diffA(n) using the LUT selected by the LUT selection
unit 350.
[0136] Fig. 8 is a flowchart of processing of calculating correction coefficients for the
n-th frame by the correction coefficient calculation unit 330 in the receiving apparatus
300. Upon receiving the n-th frame (S100), the correction coefficient calculation
unit 330 acquires RSSI1(n) and RSSI2(n) of the frame from the front end unit 112 and
the front end unit 122 to calculate the absolute value diffA of the difference between
RSSI1(n) and RSSI2(n) (S102, S104).
[0137] When there is no difference between RSSI1(n) and RSSI2(n) (S110: Yes), the correction
coefficient calculation unit 330 adds "1" to both of the first correction coefficient
α1 (n) and the second correction coefficient α2(n) (S112). As a result, the combining
unit 240 performs combining with a maximum ratio combining operation expression when
obtaining the combined signal D for each sub-carrier for each symbol of the frame.
[0138] Meanwhile, when there is a difference between RSSI1(n) and RSSI2(n) (S110: No), the
correction coefficient calculation unit 330 performs the following operation. That
is, when the strongest branch is the first branch (S120: Yes), the correction coefficient
calculation unit 330 sets RSSI1(n) as RSSI(max) and selects one LUT from LUT1 to LUT4
based on RSSI1 (n) (S122). Then, the correction coefficient calculation unit 330 adds
"1" to the first correction coefficient α1(n), and selects the correction coefficient
corresponding to diffA calculated in step S104 as the second correction coefficient
α2(n) from the LUT that is selected in step S122 (S124). As a result, the combining
unit 240 performs combining with a combining operation expression obtained by correcting
each term corresponding to the second branch in the numerator and the denominator
of the maximum ratio combining operation expression by the second correction coefficient
α2(n) when obtaining the combined signal D for each sub-carrier for each symbol of
the frame.
[0139] When the strongest branch is the second branch (S120: No), the correction coefficient
calculation unit 330 sets RSSI2(n) as RSSI (max) and selects one LUT from LUT1 to
LUT4 based on RSSI2 (n) (S132). Then, the correction coefficient calculation unit
330 adds "1" to the second correction coefficient α2(n), and selects, from the LUT
selected in step S132, the correction coefficient corresponding to diffA calculated
in step S104 as the first correction coefficient α1(n) (S134). As a result, the combining
unit 240 performs combining with a combining operation expression obtained by correcting
each term corresponding to the first branch in the numerator and the denominator of
the maximum ratio combining operation expression by the first correction coefficient
α1(n) when obtaining the combined signal D for each sub-carrier for each symbol of
the frame.
<Fourth embodiment>
[0140] As described above, the correction coefficient calculation unit 330 in the receiving
apparatus 300 according to the third embodiment specifies an intensity range of the
intensity of the reception signal of the strongest branch (RSSI(max)) based on the
thresholds T1 to T3 to select a LUT to calculate the correction coefficient. In this
example, an embodiment including a configuration regarding setting of the thresholds
T1 to T3 will be described.
[0141] Fig. 9 shows a receiving apparatus 400 according to a fourth embodiment. The receiving
apparatus also 400 also diversity-receives a transmission signal of OFDM system. Only
the difference from the receiving apparatus 300 will be described here. Further, an
operation of the receiving apparatus 400 only at a time of threshold adjustment will
be described.
[0142] In the receiving apparatus 400, a correction coefficient calculation unit 430 is
provided in place of the correction coefficient calculation unit 330. Further, since
the correction coefficient calculation unit 430 uses a decoding result of a combined
signal D when adjusting thresholds T1 to T3 in the receiving apparatus 400, a back
end unit 490 that performs processing such as decoding of the combined signal D is
shown in Fig. 9. The back end unit 490 includes a decoder such as a Viterbi decoder
that is typically included in this type of receiving apparatus. Further, the receiving
apparatus 400 includes a controller 470 to input various types of information described
later to the correction coefficient calculation unit 430, and a MAC unit 480 (MAC:
Media Access Control) that performs Cyclic Redundancy Check (CRC) processing on the
decoding result output from the back end unit 490 to output the result (OKorNG). The
result of the CRC processing by the MAC unit 480 is also input to the controller 470.
[0143] Further, the antenna 110 and the antenna 120 are connected to the outside by lines.
When thresholds are set, the antenna 110 and the antenna 120 are supplied with the
reception signal R1 and the reception signal R2 from the outside through a wired connection,
respectively, and output these signals to the front end unit 112 and the front end
unit 122.
[0144] The controller 470 receives a mode signal and a LUT number (in this example, four
from 1 to 4) from the outside, and receives results of CRC processing from the MAC
unit 480.
[0145] The correction coefficient calculation unit 430 also receives various types of data
from the controller 470 in addition to RSSI1 (n) and RSSI2(n). Information input to
the correction coefficient calculation unit 430 from the controller 470 will be described
together with a detailed configuration of the correction coefficient calculation unit
430.
[0146] Fig. 10 shows a configuration example of the correction coefficient calculation unit
430. The correction coefficient calculation unit 430 includes a strongest branch determination
unit 431, a difference calculation unit 432, a LUT storage unit 434, a LUT selection
unit 435, a correction coefficient output unit 436, a selector 442, and a threshold
adjustment unit 450. The threshold adjustment unit 450 includes a storing unit 451
and a threshold determination unit 452.
[0147] The mode signal is a signal that indicates an operation mode of the correction coefficient
calculation unit 430. The mode signal "1" indicates a "threshold adjustment mode",
and the mode signal "0" indicates a "normal operation mode". This mode signal is input
to the controller 470 from the outside, and is transmitted to the correction coefficient
calculation unit 430 by the controller 470.
[0148] In the normal operation mode, the correction coefficient calculation unit 430 performs
the similar operation as the correction coefficient calculation unit 330 in the receiving
apparatus 300.
[0149] In the threshold adjustment mode, the correction coefficient calculation unit 430
adjusts the threshold T1 to the threshold T3 that specify the range of the intensity
of RSSI (max) to select LUT1 to LUT4.
[0150] Each functional block of the correction coefficient calculation unit 430 will be
described in detail.
[0151] The strongest branch determination unit 431 receives RSSI1 (n) and RSSI2 (n), selects
one of RSSI1 (n) and RSSI2 (n) which is larger one (RSSI(max)), outputs (RSSI(max))
to the LUT selection unit 435, and outputs the number of the branch (strongest branch
number) to the correction coefficient output unit 436.
[0152] The difference calculation unit 432 receives RSSI1(n) and RSSI2(n), calculates the
absolute value diffA(n) of the difference between RSSI1(n) and RSSI2(n), and outputs
the absolute value diffA(n) to the LUT storage unit 434.
[0153] The LUT storage unit 434 stores four LUTs that are similar to LUT1 to LUT4 stored
in the LUT storage unit 340 of the correction coefficient calculation unit 330 in
the receiving apparatus 300. The LUT storage unit 434 selects the correction coefficient
(α0) corresponding to diffA from the difference calculation unit 432 from the LUT
indicated by the LUT number from the selector 442 to output the correction coefficient
(α0) to the correction coefficient output unit 436.
[0154] The correction coefficient output unit 436 outputs "1" as the correction coefficient
of the branch (strongest branch) which is the first branch or the second branch indicated
by the strongest branch number from the strongest branch determination unit 431, and
outputs the correction coefficient α0 from the LUT storage unit 434 as the correction
coefficient of the branch different from the strongest branch.
[0155] The value RSSI(max) output from the strongest branch determination unit 431 is also
input to the LUT selection unit 435. The LUT selection unit 435 holds a threshold
T1 to a threshold T3. Then, the LUT selection unit 435 specifies the range of RSSI(max)
based on these thresholds to select one LUT from LUT1 to LUT4. The LUT selection unit
435 outputs the number of the LUT that is selected to the selector 442. Further, when
receiving the threshold T1 to the threshold T3 from the threshold adjustment unit
450, the LUT selection unit 435 updates respective thresholds held therein with the
thresholds T1 to T3 that are received.
[0156] When the thresholds are set, numbers 1 to 4 indicating LUT1 to LUT4, respectively,
are successively input to the controller 470 from the outside. The controller 470
transfers the number input from the outside to the selector 442 of the correction
coefficient calculation unit 430.
[0157] The selector 442 selects and outputs one of the LUT number from the controller 470
and the output from the LUT selection unit 435 according to the mode signal. More
specifically, when the mode signal is "1", the selector 442 outputs the LUT number
from the controller 470. When the mode signal is "0", the selector 442 outputs the
number from the LUT selection unit 435. The LUT number output from the selector 442
is input to the LUT storage unit 434 and the threshold adjustment unit 450.
[0158] The threshold adjustment unit 450 operates only when the mode signal is "1", and
outputs the threshold T1 to the threshold T3 to the LUT selection unit 435.
[0159] The storing unit 451 of the threshold adjustment unit 450 receives the CRC accumulation
result from the controller 470 and stores the CRC accumulation result. This CRC accumulation
result is obtained by the controller 470 by accumulating the check results of "OK"
among the results of CRC processing obtained from the MAC unit 480. In the following
description, a result obtained by accumulating the CRC processing results of "OK"
will be simply referred to as a "CRC accumulation result".
[0160] The storing unit 451 stores the LUT number from the selector 442 associated with
RSSI(max) from the strongest branch determination unit 431.
[0161] The threshold determination unit 452 determines the threshold T1 to the threshold
T3 based on the data stored in the storing unit 451 to output the threshold T1 to
the threshold T3 to the LUT selection unit 435. Referring to Fig. 11, a specific method
when the threshold determination unit 452 determines the threshold T1 to the threshold
T3 will be described.
[0162] Fig. 11 shows examples of data acquired and stored by the storing unit 451. In Fig.
11, the leftmost column shows the intensity of the reception signal of the strongest
branch (RSSI(max)), in which the minimum value and the maximum value are P0 and PM,
respectively. The symbols A1, A2, A3, and A4 are CRC accumulation results, and the
numbers following A indicate the numbers of LUTs used when the CRC accumulation results
are obtained. Further, the alphanumeric characters in parentheses following A1, A2
and the like are RSSI(max) when the CRC accumulation results are obtained. For example,
A1(P0) indicates the CRC accumulation result when RSSI(max) is P0 and LUT1 is used.
[0163] The threshold determination unit 452 determines the threshold T1 to the threshold
T3 from the data shown in Fig. 11. Specifically, the CRC accumulation result is compared
between LUT1 and LUT2, and RSSI(max) in the boundary where the magnitude relation
of the CRC accumulation results is reversed is determined as the threshold T1. In
the example shown in Fig. 11, A1 is equal to or larger than A2 when RSSI(max) is from
P0 to (P0+n1), and A1 is smaller than A2 when RSSI(max) is equal to or larger than
(P0+n1+1). The threshold determination unit 452 thus determines (P0+n1) as the threshold
T1.
[0164] Next, the threshold determination unit 452 compares the CRC accumulation result between
LUT2 and LUT3, and determines RSSI (max) in the boundary where the magnitude relation
of the CRC accumulation results is reversed as the threshold T2. In the example shown
in Fig. 11, A2 is equal to or larger than A3 when RSSI(max) is from P0 to (P0+n2),
and A2 becomes smaller than A3 when RSSI(max) is equal to or larger than (P0+n2+1).
The threshold determination unit 452 thus determines (P0+n2) as the threshold T2.
[0165] Lastly, the threshold determination unit 452 compares the CRC accumulation result
between LUT3 and LUT4, to determine RSSI(max) in the boundary where the magnitude
relation of the CRC accumulation results is reversed as the threshold T3. In the example
shown in Fig. 11, A3 is equal to or larger than A4 when RSSI(max) is from P0 to (P0+n3),
and A3 is smaller than A4 when RSSI(max) is equal to or larger than (P0+n3+1). The
threshold determination unit 452 thus determines (P0+n3) as the threshold T3.
[0166] By setting the threshold T1 to the threshold T3 as stated above, when RSSI(max) is
from P0 to (P0+n1), the CRC accumulation result is the highest if LUT1 is used. When
RSSI(max) is larger than (P0+n1) and is equal to or smaller than (P0+n2), the CRC
accumulation result is the highest if LUT2 is used. Similarly, when RSSI(max) is larger
than (P0+n2) and is equal to or smaller than (P0+n3), the CRC accumulation result
is the highest if LUT3 is used. When RSSI (max) is larger than (P0+n3), the CRC accumulation
result is the highest if LUT4 is used.
[0167] Fig. 12 is a flowchart showing a process flow when the correction coefficient calculation
unit 430 determines the threshold T1 to the threshold T3. This processing is performed
when the mode signal is "1". When the mode signal is "0", the correction coefficient
calculation unit 430 performs the similar operation as in the correction coefficient
calculation unit 330 in the receiving apparatus 300. Description of this case will
be omitted.
[0168] The flowchart shown in Fig. 12 is an example of repeating sequential transmission
of frames to the receiving apparatus 400 the number of times corresponding to the
number of LUTs (four in this example) so that RSSI(max) has each of the values from
the minimum value P0 to the maximum value PM when the receiving apparatus 400 adjusts
the threshold T1 to the threshold T3. As shown in Fig. 12, the frame is first transmitted
to the receiving apparatus 400 so that RSSI(max) has the minimum value P0 (S202, S204).
For example, as shown in Fig. 12, the branch 1 is set to the strongest branch, and
the reception signal R1 and the reception signal R2 are transmitted to the receiving
apparatus 400 so that the intensity of the reception signal becomes (P0+m2) (in this
example, m2 is 0) for the branch 1 and the intensity of the reception signal becomes
(P0-Pd+m2) for the branch 2. Note that Pd denotes the difference of the intensities
of the reception signals of the branch 1 and the branch 2.
[0169] At this time, the LUT number "1" is input to the selector 442 of the correction coefficient
calculation unit 430 through the controller 470, and the selector 442 outputs the
LUT number "1" to the LUT storage unit 434 (S206). Further, the difference calculation
unit 432 calculates diffA (S208).
[0170] Next, the correction coefficient α1 and the correction coefficient α2 of the first
branch and the second branch are obtained (S210). Specifically, "1" is added as the
correction coefficient of the strongest branch, and the correction coefficient corresponding
to diffA calculated in step S208 is obtained from LUT (LUTm1, in this example, LUT1)
corresponding to the LUT number output from the selector 442 in step S206 as the correction
coefficient of another branch.
[0171] The MAC unit 480 then performs CRC processing on the decoding result of the combined
signal obtained using the correction coefficient α1 and the correction coefficient
α2. The controller 470 then calculates a CRC accumulation result and the storing unit
451 receives the calculation result. The storing unit 451 stores the CRC accumulation
result from the controller 470 in association with LUT1 and P0 (S212).
[0172] Processing from step S206 to step S212 is then repeated for the next receiving frame,
and the storing unit 451 stores the CRC accumulation result in association with LUT1
and (P0+1) (S214: No, S216, S204 to S212).
[0173] After that, processing of step S206 to step S212 is repeated until when RSSI(max)
becomes the maximum value PM.
[0174] As a result, a CRC accumulation result (A1) for each of different values of RSSI(max)
for LUT1 in Fig. 11 is obtained.
[0175] Subsequently, the LUT number from the outside is incremented by one (S220: No, S224),
and processing from steps S202 to S212 is repeated for LUT2.
[0176] As a result, a CRC accumulation result (A2) for each of different values of RSSI(max)
for LUT2 in Fig. 11 is obtained.
[0177] After that, processing of steps S202 to S212 is also repeated for LUT3 and LUT4,
whereby each of A3 and A4 in Fig. 11 is obtained.
<Fifth embodiment>
[0178] Fig. 13 shows a communication system 500 according to a fifth embodiment. The communication
system 500 includes a communication apparatus 510 and a plurality of communication
apparatuses 520. The communication system 500 is a communication system for movable
bodies. For example, the communication apparatus 510 is a communication apparatus
installed at a roadside, and communicates with communication apparatuses installed
in passing cars. Further, the communication apparatuses 520 are in-vehicle communication
apparatuses, and communicate with the communication apparatus 510 and the communication
apparatuses 520 installed in other cars.
[0179] The communication apparatus 510 and the communication apparatuses 520 have a similar
configuration. The communication apparatus 520 will now be described as a representative
example. Fig. 14 shows the communication apparatus 520. The communication apparatus
520 includes two antennas (antenna 110 and 120), a radio frequency (RF) unit 530,
a baseband unit 550, and a media access control (MAC) unit 800. The communication
apparatus 520 performs two-branch diversity reception at a time of reception.
[0180] The RF unit 530 includes an RF unit for first branch 532 and an RF unit for second
branch 542. The RF unit 532 performs conversion of a frequency band on a signal received
by the antenna 110 (first branch signal) to output the signal to a receiving unit
600 of the baseband unit 550. The RF unit 542 performs conversion of a frequency band
on a signal received by the antenna 120 (second branch signal) to output the signal
to the receiving unit 600.
[0181] The baseband unit 550 includes the receiving unit 600 and a transmitting unit 700.
[0182] The receiving unit 600 is the receiving apparatus 300 as shown in Fig. 6, for example.
A front end unit 612, an FFT processing unit 614, and a transmission path response
estimation unit 616 in the receiving unit 600 are similar to the front end unit 112,
the FFT processing unit 114, and the transmission path response estimation unit 116
in the receiving apparatus 300, respectively.
[0183] Further, a front end unit 622 and a transmission path response estimation unit 626
in the receiving unit 600 are also similar to the front end unit 122 and the transmission
path response estimation unit 126 in the receiving apparatus 300, respectively.
[0184] An FFT/IFFT processing unit 624 includes an inverse fast Fourier transform (IFFT)
function in addition to the similar function as the FFT processing unit 124 in the
receiving apparatus 300. This IFFT function is used for a transmission operation by
the communication apparatus 520. An FFT processing functional part of the FFT/IFFT
processing unit 624 is included in the receiving unit 600, and an IFFT processing
functional part of the FFT/IFFT processing unit 624 is included in the transmitting
unit 700.
[0185] Further, a correction coefficient calculation unit 630 and a combining unit 640 in
the receiving unit 600 are similar to the correction coefficient calculation unit
330 and the combining unit 240 in the receiving apparatus 300, respectively.
[0186] A back end unit 650 performs processing such as Viterbi decoding on a combined signal
D obtained by the combining unit 640, and outputs the decoding result to the MAC unit
800.
[0187] The transmitting unit 700 includes a front end unit 710, the IFFT processing functional
part of the FFT/IFFT processing unit 624, and a back end unit 720.
[0188] The front end unit 710 receives transmission information from the MAC unit 800, performs
processing such as coding to obtain a sub-carrier signal, and outputs the sub-carrier
signal to the FFT/IFFT processing unit 624.
[0189] The FFT/IFFT processing unit 624 performs IFFT processing on the output from the
front end unit 710 to obtain a time domain symbol signal, and outputs the symbol signal
to the back end unit 720.
[0190] The back end unit 720 converts the output from the FFT/IFFT processing unit 624 into
an OFDM-based signal, to output the OFDM-based signal to the RF unit 542.
[0191] The RF unit 542 performs frequency band conversion processing inverse to the processing
at the time of reception on the signal from the back end unit 720, and transmits the
signal after the processing through the antenna 120.
[0192] The MAC unit 800 performs processing of a MAC layer, and is similar to that included
in this type of communication apparatus. Detailed description thereof will be omitted.
[0193] While the receiving apparatus 300 has been used as the receiving unit 600 as an example
in the communication system 500, the receiving apparatus according to any one of the
embodiments stated above may be used as the receiving unit 600. As a matter of course,
it is possible to obtain all the effects of the receiving apparatus that is used.
[0194] While the invention has been described in terms of several embodiments, those skilled
in the art will recognize that the invention can be practiced with various modifications
within the scope of the appended claims and the invention is not limited to the examples
described above.
[0195] For example, these embodiments can be combined as desirable by one of ordinary skill
in the art.
[0196] Further, the scope of the claims is not limited by the embodiments described above.
1. Empfangsvorrichtung, die ein Übertragungssignal eines orthogonalen Frequenzmultiplexsystems
über Diversitätsempfang empfängt, wobei die Vorrichtung Folgendes umfasst:
eine Korrekturkoeffizientenberechnungseinheit, die Korrekturkoeffizienten gemäß einer
Größenbeziehung einer Intensität eines Empfangssignals von jedem Zweig erhält, wobei
die Korrekturkoeffizienten in Zweigen mit geringeren Empfangssignalintensitäten kleiner
sind;
eine Fourier-Transformationseinheit, die eine Fourier-Transformation auf dem Empfangssignal
für jeden Zweig ausführt, um Sub-Trägersignale, die jeweiligen Sub-Trägern entsprechen,
auszugeben;
eine Übertragungspfadantwortschätzungseinheit, die eine Übertragungspfadantwort für
jedes der Sub-Trägersignale für jeden Zweig schätzt; und
eine Kombinierungseinheit, die für jeden Sub-Träger, wenn ein kombiniertes Signal
durch ein Maximalverhältniskombinieren durch Ausführen einer gewichteten Addition
auf dem Sub-Trägersignal von jedem Zweig auf Basis der durch die Übertragungspfadantwortschätzungseinheit
geschätzten Übertragungspfadantwort von jedem Zweig erhalten wird, einen Gewichtungskoeffizienten
mit jedem der durch die Korrekturkoeffizientenberechnungseinheit berechneten Korrekturkoeffizienten
korrigiert;
worin die Korrekturkoeffizientenberechungseinheit eine Intensität eines an einem Anfang
eines Rahmens des Empfangssignals bereitgestellten Synchronisationssignals als eine
Intensität des Empfangssignals von jedem in dem Rahmen beinhalteten Symbol verwendet;
worin die Empfangsvorrichtung ferner Folgendes umfasst:
einen A/D-Wandler, der das Empfangssignal in ein digitales Signal für jeden Zweig
umwandelt, um das digitale Signal der Fourier-Transformationseinheit zuzuführen; und
eine AGC-Einheit, die eine automatische Verstärkungssteuerung (AGC) für jeden Zweig
ausführt, um eine Verstärkung der Empfangssignaleingabe in den A/D-Wandler einzustellen;
worin die Korrekturkoeffizientenberechnungseinheit eine Intensität einer kurzen Präambel
in einem Rahmen des durch die AGC-Einheit erhaltenen Empfangssignals als eine Intensität
des Synchronisationssignals verwendet;
worin die Korrekturkoeffizientenberechungseinheit einen Maximalkorrekturkoeffizienten
für den stärksten Zweig hinzuaddiert, der ein Zweig ist, der die größte Empfangssignalintensität
aufweist, und für jeden der anderen Zweige denjenigen Korrekturkoeffizienten erhält,
der gleich oder kleiner als der Maximalkorrekturkoeffizient gemäß einer Differenz
in den Intensitäten des Zweiges und des stärksten Zweiges ist;
worin die Korrekturkoeffizientenberechnungseinheit für jeden der anderen Zweige den
Korrekturkoeffizienten erhält, sodass die Korrekturkoeffizienten bei zunehmender Intensität
des stärksten Zweiges größer werden;
worin die Empfangsvorrichtung ferner Folgendes umfasst:
eine Vielzahl von Nachschlagetabellen (LUTs), die eine entsprechende Beziehung zwischen
einer Differenz in der Intensität und dem Korrekturkoeffizienten anzeigen, der für
jeden aus einer Vielzahl von den durch eine Vielzahl von Schwellenwerten spezifizierten
Intensitätsbereichen eingestellt ist, worin
in jeder der LUTs der Korrekturkoeffizient bei zunehmender Differenz in der Intensität
kleiner wird,
in der Vielzahl von LUTs die Korrekturkoeffizienten in den LUTs in den für die Intensitätsbereiche
eingestellten LUTs größer sind, wobei diese Intensitätsbereiche größeren Intensitäten
mit Bezug auf dieselbe Differenz in der Intensität entsprechen, und
die Korrekturkoeffizientenberechnungseinheit für jeden der anderen Zweige die für
den Intensitätsbereich, der die Intensität des stärksten Zweigs umfasst, eingestellte
LUT auswählt, um den Korrekturkoeffizienten durch die LUT, die ausgewählt ist, zu
erhalten;
worin die Empfangsvorrichtung ferner eine Back-End-Einheit umfasst, die ein Verarbeiten
ausführt, das ein Dekodieren auf dem durch die Kombinierungseinheit erhaltenen, kombinierten
Signal umfasst, und
worin die Korrekturkoeffizientenberechnungseinheit geeignet ist, die Vielzahl von
Schwellenwerten auf Basis eines Ergebnisses einer periodischen Redundanzüberprüfungs
(CRC) -Verarbeitung für ein durch die Back-End-Einheit erhaltenes Dekodierungsergebnis
einzustellen.
2. Empfangsvorrichtung gemäß Anspruch 1, worin
die Kombinierungseinheit das Sub-Trägersignal von jedem Zweig durch eine Operation
gemäß einem Kombinierungsoperationsausdruck kombiniert, und
der Kombinierungsoperationsausdruck ein Ausdruck ist, der durch Multiplizieren von
jedem der Terme eines Zähleranteils und eines Nenneranteils eines polynomialen Ausdrucks,
der aus Termen gebildet ist, die den jeweiligen Übertragungspfadantworten der Zweige
in einem Maximalverhältniskombinierungsoperationsausdruck entsprechen, der ein Operationsausdruck
beim Maximalverhältniskombinieren ist, mit dem Korrekturkoeffizienten erhalten wird,
der für einen dem Term entsprechenden Zweig durch die Korrekturkoeffizientenberechnungseinheit
berechnet ist.
3. Empfangsvorrichtung gemäß Anspruch 1, worin die Kombinierungseinheit die durch die
Übertragungspfadantwortschätzungseinheit geschätzte Übertragungspfadantwort von jedem
Zweig korrigiert, indem sie diese mit dem durch die Korrekturkoeffizientenberechnungseinheit
berechneten Korrekturkoeffizienten des Zweiges multipliziert, um einen Gewichtungskoeffizienten
zu berechnen, wenn das Sub-Trägersignal von jedem Zweig bei einem maximalen Verhältnis
unter Verwendung der Übertragungspfadantwort von jedem Zweig nach Korrektur kombiniert
wird.
4. Kommunikationsvorrichtung, umfassend:
eine Übertragungseinheit, die ein Übertragungssignal eines orthogonalen Frequenzmultiplexsystems
erzeugt und sendet; und
eine Empfangseinheit, die das Übertragungssignal eines orthogonalen Frequenzmultiplexsystems
über Diversitätsempfang empfängt,
worin die Empfangseinheit die Empfangsvorrichtung gemäß Anspruch 1 ist.
5. Kommunikationssystem, umfassend eine Vielzahl von Kommunikationsvorrichtungen, die
das Senden oder das Empfangen eines Übertragungssignals eines orthogonalen Frequenzmultiplexsystems
ausführen,
worin mindestens eine der Kommunikationsvorrichtungen die Empfangsvorrichtung gemäß
Anspruch 1 umfasst.
6. Empfangsvorrichtung, die ein Übertragungssignal eines orthogonalen Frequenzmultiplexsystems
über Diversitätsempfang empfängt, wobei die Empfangsvorrichtung Folgendes umfasst:
eine Antenne für jeden Zweig;
eine Front-End-Einheit, die ein durch die Antenne empfangenes Empfangssignal empfängt
und ein Verarbeiten umfasst, das eine A/D-Wandlung und eine automatische Verstärkungssteuerungs
(AGC) -Verarbeitung umfasst, die eine Verstärkung des der A/D-Wandlung ausgesetzten
Empfangssignals einstellt;
eine Fourier-Transformationseinheit, die eine Fourier-Transformation auf einem durch
die Front-End-Einheit erhaltenen, digitalen Signal ausführt, um Sub-Trägersignale
auszugeben, die jeweiligen Sub-Trägern entsprechen; und
eine Übertragungspfadantwortschätzungseinheit, die eine Übertragungspfadantwort für
jedes der aus der Fourier-Transformationseinheit ausgegebenen Sub-Trägersignale schätzt,
wobei die Empfangsvorrichtung ferner Folgendes umfasst:
eine Korrekturkoeffizientenberechnungseinheit, die eine Intensität des an der Front-End-Einheit
von der Front-End-Einheit von jedem Zweig erhaltenen Empfangssignals empfängt, um
Korrekturkoeffizienten gemäß einer Größenbeziehung der Intensität des Empfangssignals
von jedem Zweig zu erhalten, wobei die Korrekturkoeffizienten in Zweigen mit geringeren
Empfangssignalintensitäten kleiner sind; und
eine Kombinierungseinheit, die mit der Korrekturkoeffizientenberechnungseinheit und
der Fourier-Transformationseinheit und der Übertragungspfadantwortschätzungseinheit
von jedem Zweig verbunden ist, und für jeden Sub-Träger, wenn ein kombiniertes Signal
durch Ausführen eines Maximalverhältniskombinierens durch Ausführen einer gewichteten
Addition auf dem Sub-Trägersignal von jedem Zweig auf Basis der durch die Übertragungspfadantwortschätzungseinheit
geschätzten Übertragungspfadantwort von jedem Zweig erhalten wird, einen Gewichtungskoeffizienten
mit jedem der durch die Korrekturkoeffizientenberechnungseinheit berechneten Korrekturkoeffizienten
korrigiert;
worin die Korrekturkoeffizientenberechnungseinheit eine Intensität eines an einem
Anfang eines Rahmens des Empfangssignals bereitgestellten Synchronisationssignals
als eine Intensität des Empfangssignals von jedem in dem Rahmen beinhalteten Symbol
verwendet;
worin die Korrekturkoeffizientenberechungseinheit eine Intensität einer kurzen Präambel
in einem Rahmen des durch die Front-End-Einheit erhaltenen Empfangssignals in der
AGC-Verarbeitung als die Intensität des Synchronisationssignals verwendet;
worin die Korrekturkoeffizientenberechungseinheit einen Maximalkorrekturkoeffizienten
für den stärksten Zweig hinzuaddiert, der ein Zweig ist, der die größte Empfangssignalintensität
aufweist, und für jeden der anderen Zweige den Korrekturkoeffizienten erhält, der
gleich oder kleiner als der Maximalkorrekturkoeffizient gemäß einer Differenz in den
Intensitäten des Zweiges und des stärksten Zweiges ist;
worin die Korrekturkoeffizientenberechnungseinheit für jeden der anderen Zweige den
Korrekturkoeffizienten erhält, sodass die Korrekturkoeffizienten bei zunehmender Intensität
des stärksten Zweiges größer werden;
worin die Empfangsvorrichtung ferner Folgendes umfasst:
eine Vielzahl von Nachschlagetabellen (LUTs), die eine entsprechende Beziehung zwischen
einer Differenz in der Intensität und dem für jeden aus einer Vielzahl von den durch
eine Vielzahl von Schwellenwerten spezifizierten Intensitätsbereichen eingestellten
Korrekturkoeffizienten anzeigen, worin
in jeder der LUTs der Korrekturkoeffizient bei zunehmender Differenz in der Intensität
kleiner wird,
in der Vielzahl von LUTs die Korrekturkoeffizienten in den LUTs in den für die Intensitätsbereiche
eingestellten LUTs größer sind, wobei die Intensitätsbereiche großen Intensitäten
mit Bezug auf dieselbe Differenz in der Intensität entsprechen, und
die Korrekturkoeffizientenberechnungseinheit für jeden der anderen Zweige die für
den Intensitätsbereich, welche die Intensität des stärksten Zweiges umfasst, eingestellte
LUT auswählt, um den Korrekturkoeffizienten durch die LUT, die ausgewählt ist, zu
erhalten;
worin die Empfangsvorrichtung ferner eine Back-End-Einheit umfasst, die ein Verarbeiten
ausführt, das ein Dekodieren auf dem durch die Kombinierungseinheit erhaltenen kombinierten
Signal ausführt,
worin die Korrekturkoeffizientenberechnungseinheit geeignet ist, die Vielzahl von
Schwellenwerten auf Basis eines Ergebnisses einer periodischen Redundanzüberprüfungs
(CRC) -Verarbeitung für ein Ergebnis des durch die Back-End-Einheit erhaltenen Dekodierens
einzustellen.
7. Empfangsvorrichtung gemäß Anspruch 6, worin
die Kombinierungseinheit das Sub-Trägersignal von jedem Zweig durch eine Operation
gemäß einem Kombinierungsoperationsausdruck kombiniert, und
der Kombinierungsoperationsausdruck ein Ausdruck ist, der durch Multiplizieren von
jedem Term eines Zähleranteils und eines Nenneranteils eines polynomialen Ausdrucks,
der aus Termen gebildet ist, die den jeweiligen Übertragungspfadantworten der Zweige
in einem Maximalverhältniskombinierungsoperationsausdruck entsprechen, der ein Operationsausdruck
beim Maximalverhältniskombinieren ist, mit dem Korrekturkoeffizienten erhalten wird,
der für einen dem Term entsprechenden Zweig durch die Korrekturkoeffzientenberechnungseinheit
berechnet ist.
8. Empfangsvorrichtung gemäß Anspruch 6, worin die Kombinierungseinheit die durch die
Übertragungspfadantwortschätzungseinheit geschätzte Übertragungspfadantwort von jedem
Zweig korrigiert, indem sie diese mit dem durch die Korrekturkoeffizientenberechnungseinheit
berechneten Korrekturkoeffizienten multipliziert, um einen Gewichtungskoeffizienten
zu berechnen, wenn das Sub-Trägersignal von jedem Zweig bei einem maximalen Verhältnis
unter Verwendung der Übertragungspfadantwort von jedem Zweig nach Korrektur kombiniert
wird.